CPI / API Oil-Water Separator
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CPI / API Oil-Water Separator Calculator

Plate Pack & Gun-Barrel Sizing per API Publication 421

Size a Corrugated Plate Interceptor or open API gun-barrel separator. Stokes-law rising-droplet velocity governs; the Hazen overflow-rate basis sets the required horizontal projected area. CPI plate packs reduce the effective settling distance and cut the vessel footprint by 5–10× vs. a simple basin.

Process Stream

BWPD
mg/L
mg/L
µm
CPI: 30–80; API gun-barrel: 150
—
°API
°F
cP

Plate Pack

mm
°
ft
ft

Vessel

ft
Oil layer + sediment allowance
ft
Sand / solids accumulation

📚 Learn the Theory

API 421 design basis, Stokes settling, plate-pack geometry, Reynolds re-entrainment threshold.

Read Engineering Guide →

Sizing Method

Stokes oil-droplet rise (ft/s):

Vt = 1.78 × 10−6 · dm2 · ΔSG / μw

Required horizontal area (Hazen):

Ah = Q (ft3/s) / Vt (ft/s)

CPI horizontal projection per plate:

Ah,plate = L · W · cos(θ)

Total CPI Ah:

Ah,total = nplates · nmodules · Ah,plate

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